Peroxidic compositions

ABSTRACT

Compositions for the polymer curing, comprising: 
     a) one or more organic peroxides and 
     b) 3,7-Dimethyl-1,3,6-Octatriene (OCIMENE).

The present invention relates to peroxidic compositions usable for theelastomer and polyolefin curing in general, having an improved scorchresistance without negatively affecting in a meaningful way the curingefficiency.

More specifically it relates to compositions having a longer scorch timeas shown by the ts₅ and ts₁₀ values combined with a good curing densityas shown by the MH values and having t₉₀ curing times of the same order.

It is well known that organic peroxides are used for the elastomer andpolyolefin curing. However it is desirable to have availablecompositions with higher scorch times in order to increase the compoundprocessability avoiding precuring phenomena.

In order to solve this technical problem organic peroxides having alonger half-time could be used, however this has the drawback tolengthen also the curing times (t₉₀), to the detriment, therefore, ofthe productivity, in order to maintain the same curing value (MH).

Adding additives to the peroxidic compositions to increase the scorchtime is also known. See for example DE 2,553,145 and 2,553,094 whereinperoxides with different scorch times are mixed but the drawback is thatthe curing times become longer with the above mentioned disadvantages.

Also amine-based additives are known, but today they cannot be used anylonger since they are considered toxicologically dangerous due to theircancerogenous effects.

There are also known hydroquinones, e.g. di-t-butyl or di-t-amyl,sulphur-based compounds, or antioxidants in general as scorch retardantsin the peroxidic curing, in this way however the final properties of thecured product are poor since the MH value becomes worse.

In U.S. Pat. No. 5,292,791 and U.S. Pat. No. 5,245,084 a peroxidiccomposition having scorch retardant properties is described, whichcomprises:

a) a peroxide

b) an hydroquinone derivative

c) a curing promoter.

A scorch resistant composition, stable upon storage, is also known fromthe EP 785,229 in the name of the Applicant wherein a powdered peroxideor in the form of grain or masterbatch is mixed at the time of use witha masterbatch comprising an inhibitor and a curing promoter. In theabove compositions of the European Patent Application and of the U.S.Pat. No. '791 and '084 two additives are used. One mainly acts asinhibitor (scorch resistant) but has a negative effect on the curingdegree.

In order to maintain the curing degree a curing promoter is added.

From the EP 533,089 peroxidic compositions are known wherein a solidperoxide bis(alpha t-butyl-peroxy-isopropyl)-benzene, known asPEROXIMONO F, is mixed with bis (alpha t-amyl peroxy-isopropyl)-benzene,known as PEROXIMON® 180. Said compositions are liquid also attemperatures of 15° C. or lower and show a low volatility. The advantageof said compositions consisted in having available particularly desiredliquid compositions in compounding application according to continous(not batch) processes or in peroxide additions carried out by directabsorption on the polymers. The drawback of these compositions is thateven though they maintain good MH values, they are not scorch resistant.

The need was felt to have available compositions with improved scorchtime without notably lower the curing density (MH) with comparable t₉₀curing times.

The Applicant has unexpectedly and surprisingly found compositions forthe polymer curing which give the above mentioned property combinationcomprising:

a) one or more organic peroxides selected from the following generalformulae:

(R¹—C(CH₃)₂—OO—C(CH₃)₂)_(n)—R²  (I)

 wherein R¹ is an alkyl, aryl and aryl-alkyl-substituted group havingfrom 1 to 9 carbon atoms; R² is selected from phenylene, ethylene,—C═C—, —C═C—, alkyl, aryl and aryl-alkyl-substituted group; said groupshaving from 1 to 9 carbon atoms; n is an integer equal to 1 or 2;

wherein the two R³ substituents are independently alkyl, aryl,aryl-alkyl-substituted groups having from 1 to 9 carbon atoms, R⁴ and R⁵are independently linear or branched, when possible, alkyl groups,having from 1 to 6 carbon atoms or —(CH₂)_(m)—C(O)OR⁶ wherein R⁶ is analkyl group from 1 to 4 carbon atoms; m is an integer from 1 to 3, orthey jointly form a not substituted or substituted cyclohexane orcyclododecane ring with 1 up to 3 alkyl groups having from 1 to 4 carbonatoms; and

b) 3,7-Dimethyl-1,3,6-Octatriene (OCIMENE).

The preferred type a) components are: dicumylperoxide (PEROXIMONO®(DC)), t-butyl-cumylperoxide (PE-ROXIMON® 801),bis(α-t-butylperoxyisopropyl)benzene (PEROXIMOND® F),2,5-di(t-butylperoxy)-2,5-dimethylhexane (Luperoxo 231),2,5-di(t-butylperoxy)-2,5-dimethylhexine-3 (Luperox® 130),diterbutylperoxide (Luperox® DI), 1,1-di(terbutylpero-xy)-3,3,5-trimethylcyclohexane (Luperox®101),n-butyl-4,4-di-(terbutylperoxy)valerate (Luperox® 230),1,1-di-terbutylpe-roxycyclohexane (Luperox® 331),isopropylcumylterbutylperoxide (PEROXIMON® DC 60),bis(α-teramylperoxyisopropyl)benzene (PEROXIMON® 180). All theseperoxides are commercialized by Elf Atochem.

The component b) amount for one hundred parts by weight (100 phr) ofelastomer or polyolefin to be cured is in the range 0.05-1.7, preferably0.1-1.3.

The weight ratio between the component a) and the component b) is in therange 1:0.02 to 1:0.7, preferably 1:0.05 and 1:0.6.

The compound b) is usually a mixture of isomers cis/trans as sold byFluka in the name of ocimene.

It is also possible to prepare formulations (in inert fillers and/orpredispersions in a polymer) containing the (a+b) mixture in an amountgenerally higher than or equal to 30% to be used as additives to bedispersed in the polymer to be cured. The preferred range for saidformulations is from 30 to 70% of (a+b) mixture. Said formulations arewell known and can be prepared according to EP 785,229 hereinincorporated by reference.

The polymers which can be cured according to the present invention areethylene-based polymers. More specifically polyethylene having average,low, high density, poly-butene-1, ethylene/vinyl-acetate copolymers,acrylic ester/ethylene copolymers, ethylene/propylene copolymers,ethylene/butene-1 copolymers, ethylene/4-methyl-pentene-1 copolymers andpropylene/butene-1 copolymers; furthermore ethylene/propylene EP or EPDMtype elastomeric polymers or copolymers, butyl rubber, chlorinatedpolyethylene and propylene/butene-1 copolymer, can be mentioned. Alsomixtures of two or more polymers can be used.

The final compound ready for curing (polymer+peroxide a)+additiveb)+mineral and non mineral fillers, antioxidants, curing coagents, etc.,see the above mentioned EP 785,229, is preferably used to producemanufactured articles extruded in a continous way and/or injectionand/or compression molded.

Curing can be carried out by heat and can be directly performed in themolding in the case of compression or injection molding; in the case ofcontinuous extrusion with the known methods, for example vapour,nitrogen, melted salt baths, autoclaves curing lines, etc.

The polymer characterization in terms of scorch resistance (ts₅ andts₁₀), curing rate (t₉₀) and curing density (MH) of the cured product,is reported in Example 1.

The following examples are given for illustrative purposes and they arenot limitative of the present invention.

EXAMPLE 1

A blend was prepared by mixing 100 g of low density polyethylene(produced by ELF ATOCHEM, commercialized as LACQTENEO® 1020 FN 24),under the form of fine powder, and 2.5 g of dicumylperoxide (PEROXIMON®DC) and 0.3 g of 3,7-Dimethyl-1,3,6-Octatriene (OCIMENE).

The blend was prepared in a V mixer at 50° C. for 60 minutes.

The resulting blend was characterized by using a rheometer(α-Technologies and commercialized as ODR 2000) and a Mooney viscometerfor the scorch tests (MV 2000 α-Technologies).

MH and t₉₀ have been obtained by the ODR curve at 180° C. (oscillationarc 3°, oscillation frequency 100 cycles/min.). The ts₅ and ts₁₀ scorchtimes have been obtained by the scorch curve carried out by theviscometer MV 2000 at 160° C.

The t₉₀ term means the necessary time to reach a curing equal to 90%respectively of the curing curve maximum. MH represents the maximumcouple on the same curve.

By ts₅ and ts₁₀ scorch time, the necessary time to obtain a viscosityincrease of 5 or 10 Mooney units, with respect to the minimum value, ismeant.

The results are shown in Table 1.

EXAMPLE 1A (comparative)

The procedure of Example 1 has been repeated without using the componentb) 3,7-Dimethyl-1,3,6-Octatriene (OCIMENE).

The results are reported in Table 1.

By comparing Example 1 with Example 1A it is noticed that Example 1shows a good MH value, with comparable t₉₀, but the scorch time isclearly higher with the invention composition.

EXAMPLE 2

Example 1 has been repeated but using 1 g of component b).

The results are shown in Table 1.

The comparison with the results of Example 1 and 1A shows an improvementof the scorch time and MH values which have not substantially worsened.

TABLE 1 Peroxide Ex. (comp a)) Comp. b) ts₅ ts₁₀ t₉₀ MH No. (g) (g) (s)(s) (s) (lb. inch) 1 DC 2.5 0.3 281 372 395 18.72 1A DC 2.5 0 192 218377 21.7 2 DC 2.5 1 339 390 388 18.73

EXAMPLES 3-9

Example 1 has been repeated but by using the amount of the peroxidecompound (DC) and component b) reported in Table 2.

The blend was characterized by the measurement of ts₅ at 145° C. withthe Mooney viscosimeter of Example 1.

TABLE 2 Peroxide (DC) Comp. b) ts₅ Ex. No. (g) (g) (145° C.) 3 2.0 0 5484 2.0 0.3 790 5 2.0 1.0 1080 6 2.0 1.5 1368 7 1.5 0 661 8 1.5 0.3 1057 91.5 1.0 1552

The data in Table 2 show that the additive b) provides an umprovedscorch protection (ts₅) at 145° C. This is extremely relevant since atemperature around 145° C. is the processing temperature of the finalcompound to obtain manufactured articles by extrusion.

This allows the user of this technology to enhance the productivity andthe final product stability during the extrusion process.

EXAMPLE 3A-9A (comparatives)

The procedure of Examples 3-9 has been repeated using as the componentb) trans,trans-2,6-dimethyl-2,4,6-octatriene.

The results are shown in Table 2A.

TABLE 2A Peroxide (DC) Comp. b) ts₅ Ex. No. (g) (g) (145° C.) 3A 2.0 0548 4A 2.0 0.3 778 5A 2.0 1.0 1025 6A 2.0 1.5 1327 7A 1.5 0 661 8A 1.50.3 1012 9A 1.5 1.0 1380

The results of Table 2A show that in comparative examples 3A-9A ts₅ islower, at a same concentration of component b), than the correspondingexamples according to the present invention.

What is claimed is:
 1. A composition suitable for polymer curing comprising: a) one or more organic peroxides selected from the following general formulae: (R¹—C(CH₃)₂—OO—C(CH₃)₂)_(n)—R²  (I)  wherein R¹ is an alkyl, aryl and aryl-alkyl-substituted group having from 1 to 9 carbon atoms, R² is selected from the group consisting of phenylene, ethylene, —C═C—, —C═C—, alkyl, aryl and aryl-alkyl-substituted group; said groups having from 1 to 9 carbon atoms; n is an integer equal to 1 or 2; and

wherein the two R³ substituents are independently alkyl, aryl, aryl-alkyl-substituted groups having from 1 to 9 carbon atoms, R⁴ and R⁵ are independently linear or branched, when possible, alkyl groups, having from 1 to 6 carbon atoms or —C(CH₂)_(m)—C(O)OR⁶ wherein R⁶ is an alkyl group from 1 to 4 carbon atoms; m is an integer from 1 to 3, or they jointly form an unsubstituted or a substituted cyclohexane or cyclododecane ring with 1 up to 3 alkyl groups having from 1 to 4 carbon atoms; and b) 3,7-Dimethyl-1,3,6-Octatriene.
 2. The composition according to claim 1 wherein the component a) is selected from: dicumylperoxide, t-butyl-cumylperoxide, bis(α-t-butylperoxyisopropyl)benzene, 2,5-di(t-butylperoxy)-2,5-dimethylhexane, 2-5-di(t-butylperoxy)-2,5-dimethylhexine-3,diterbutylperoxide, 1,1-di(terbutylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-di(terbutylperoxy)valerate, 1,1-di-terbutylperoxycyclohexane, isopropylcumylterbutylperoxide and bis(α-teramylperoxyisopropyl)benzene.
 3. The composition according to claim 1 wherein the weight ratio between the component a) and the component b) is in the range 1:0.02 to 1:0.7.
 4. A composition comprising a polymer to be cured and the composition according to claim 1 and optionally mineral and non mineral fillers, antioxidants and/or curing coagents.
 5. The composition according to claim 4 wherein the component b) amount for one hundred parts by weight (100 phr) of polymer to be cured is in the range 0.05-1.7.
 6. The composition according to claim 5 wherein the component b) amount for one hundred parts by weight (100 phr) of polymer to be cured is in the range 0.01-1.3.
 7. The composition according to claim 4 wherein the polymer to be cured is selected from the group consisting of polymers based on ethylene, poly-butene-1 and propylene/butene-1 copolymers.
 8. The composition according to claim 7 wherein the ethylene-based polymer to be cured is selected from the group consisting of polyethylene having average, low, high density, ethylene/vinyl-acetate copolymers, acrylic ester/ethylene copolymers, ethylene/propylene copolymers, ethylene/butene-1 copolymers and ethylene/4-methyl-pentene-1 copolymers.
 9. The composition according to claim 4 wherein the polymer to be cured is selected from the group consisting of ethylene/propylene or ethylene/propylene/diene elastomeric polymers or copolymers, butyl rubber, chlorinated polyethylene and propylene/butene-1 copolymer.
 10. The composition according to claim 3 wherein the weight ratio between the component a) and the component b) is in the range 1:0.05 to 1:0.6. 